fix(port/fsdev): address N32H4x glue review findings

- usb_glue_nation.c: match usb_dc_low_level_init/deinit to the (void)
  weak stubs in usb_dc_fsdev.c and guard on g_usbdev_bus[0] (the old
  (uint8_t busid) signature read garbage at the no-arg call site)
- usb_glue_nation.c: drop NVIC_PriorityGroupConfig from the driver hook;
  it reprograms SCB->AIRCR for the whole system, priority grouping now
  stays with board/application startup code
- usb_glue_nation.c: derive the USBFS prescaler from SystemCoreClock at
  runtime instead of a per-part compile-time table (fixes N32H475
  landing in the 240 MHz branch; adapts to any configured PLLCLK)
- add docstrings to the functions touched by this diff

0 files changed, 0 insertions, 0 deletions